Laminated piezoelectric element, actuator and printing head

ABSTRACT

The laminated piezoelectric element having a thickness of 100 μm or less of the present invention comprises a laminate which comprises a plurality of piezoelectric ceramic layers  1 , and electrodes  2,3  provided the surface and the inside of the laminate, wherein the electrode  2  comprises a silver-palladium alloy containing 71 to 99.9% by volume of silver and 0.1 to 29% by volume of palladium.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a laminated piezoelectricelement, an actuator and a printing head and, more particularly, to alaminated piezoelectric element and an actuator that are suitable forthe piezoelectric sensor of, for example, fuel injector, ink jetprinter, piezoelectric resonator, oscillator, ultrasonic motor,ultrasonic oscillator, filter, acceleration sensor, knocking sensor, AEsensor or the like, and can be advantageously used particularly for aprinting head that utilizes vibration of 2-dimensional vibration ofexpansion and contraction or linear vibration in longitudinal directionor in the direction of the thickness.

[0003] 2. Description of Related Art

[0004] Piezoelectric ceramics materials have been used in, for example,actuator, filter, piezoelectric resonator (oscillator included),ultrasonic oscillator, ultrasonic motor and piezoelectric sensor.

[0005] Among these devices, the piezoelectric actuator is used as thepositioning actuator for an X-Y stage of semiconductor manufacturingequipment, the actuator for the printing head of ink jet printer or thelike, by making advantage of the very high response of the piezoelectricelement to electrical signals, in the order of micro seconds. Especiallywith the recent trend of color printers toward higher printing speed andlower prices, piezoelectric elements are under increasing demand for theapplication to the ink discharging actuator of ink jet printer or thelike.

[0006] For example, Japanese Unexamined Patent Publication No. 11-121820discloses an actuator that uses a silver-palladium alloy for internalelectrode. This actuator is manufactured in such a process as: First, anelectrically conductive paste is printed on the surface of a green sheetmade of a piezoelectric ceramic material as the major component with athickness of 200 μm so as to form internal electrodes, 200 green sheetsare stacked one on another with the side on which the internalelectrodes are printed facing upward, a set of five green sheets withoutthe electrode paste printed thereon is stacked on each side of thestack, on top and bottom, and the resultant stack is pressed to make alaminate. Then the laminate is processed to remove binder contained inthe green sheets and in the internal electrodes, and is sintered to makea sintered laminate. An insulator, external electrodes and lead wiresare connected to the sintered laminate, thereby to complete theactuator.

[0007] The actuator that is made as described above has an advantagethat it is easy to make the multi-layer laminate of the piezoelectricceramic material and the electrode material and that the actuator can bemanufactured at a low cost, and therefore has been preferably used asthe actuator for the printing head of ink jet printer, the positioningactuator for X-Y stage and the like.

[0008] Unfortunately, the actuator disclosed in Japanese UnexaminedPatent Publication No. 11-121820 is relatively large in thickness whichimposes a limitation to the amount of displacement, resulting in aproblem that large displacement cannot be achieved. Moreover, there isalso a problem of deteriorating characteristic of the actuatordisplacement, thus resulting in a marked decrease in the displacement ofthe printing head.

[0009] In high resolution printers which have been showing remarkableprogress recently, in particular, thinner piezoelectric ceramic layersare employed in order to achieve greater displacement of the actuator.In the case of a thin actuator made by stacking piezoelectric ceramiclayers each measuring several tens of micrometers or less in thicknessor an actuator having a total thickness of 100 μm or less, on the otherhand, there is such a problem that shrinkage of the internal electrodescaused during sintering results in significant deformation because theactuator is very thin.

[0010] There is also such a problem that d constant varies significantlyacross a single element, since residual stress is distributed unevenlyacross the actuator by uneven shrinkage of the internal electrodes. Insuch a thin actuator as described above, in particular, in case aplurality of displacement elements are mounted on a single circuitboard, significant variations beyond ±10% occur in the amount ofdisplacement among the actuators. It requires an expensive IC to controlthe operation of the actuators having such significant variations, thusresulting in an increase in the manufacturing cost of the printing heador the printer, while requiring complicated control scheme.

SUMMARY OF THE INVENTION

[0011] Accordingly, an object of the present invention is to provide alaminated piezoelectric element and an actuator that are capable ofmaking larger displacement with less variation in the displacement.

[0012] Another object of the present invention is to provide a printinghead that has a better displacement characteristic and is capable ofprinting with higher picture quality and higher resolution.

[0013] The present inventors have found that, in the case of a laminatedpiezoelectric element having a thickness larger than 100 μm, shrinkageof the electrode occurs in the direction of the thickness thus resultingin less residual stress within the surface since the piezoelectricceramic layer has a greater thickness compared to that of the electrode,while in the case of a laminated piezoelectric element having athickness within 100 μm, shrinkage of the electrode has an influenceover the entire laminated piezoelectric element and causes a differencein shrinkage between the electrode and the piezoelectric ceramic layer,thus resulting in a significant residual stress remaining aftersintering.

[0014] Based on this finding, the present inventors have further studiedand reached another finding that it is made possible to decrease theresidual stress in the laminated piezoelectric element and prevent itfrom deforming by improving the wettability of the paste to form theelectrode and the piezoelectric ceramic layer thereby increasing thebonding between these members, so that uniform distribution of the dconstant (piezoelectric strain constant) across the actuator surface canbe obtained.

[0015] Specifically, the laminated piezoelectric element having athickness of 100 μm or less of the present invention comprises alaminate which comprises a plurality of piezoelectric ceramic layers,and electrodes provided at least one of the surface and the inside ofsaid laminate, wherein said electrodes comprises a silver-palladiumalloy containing 71 to 99.9% by volume of silver and 0.1 to 29% byvolume of palladium. This laminated piezoelectric element can make alarge displacement because of a small thickness, while variations indisplacement are small because of reduced residual stress. As a result,the laminated piezoelectric element and the actuator thus obtained alloweasy control of displacement and provide stable piezoelectriccharacteristic.

[0016] The electrodes of the laminated piezoelectric element accordingto the present invention preferably comprises a silver-palladium alloythat contains 87% by volume or more silver and has residual stress of100 MPa or less remaining inside. When the silver-palladium alloycontaining 87% by volume or more silver is used and the firingconditions are controlled, higher effect of reducing the residual stresscan be obtained and a laminated piezoelectric element having betterdisplacement characteristic can be made, so that a high performanceprinting head can be made when used as an actuator.

[0017] The piezoelectric ceramic layer preferably contains Pb, whichenables it to improve the wettability between the piezoelectric ceramiclayer and the silver-palladium alloy that makes the electrodes.

[0018] It is also preferable that the electrodes include piezoelectricceramic material, and the proportion of the silver-palladium alloy tothe piezoelectric ceramic material is in a range from 100: 16 to 60.This constitution further improves the bonding strength between theelectrode and the piezoelectric ceramic layer so as to effectivelyrestrict the deformation of the piezoelectric ceramic element andmaintain a low electrical conductivity.

[0019] It is also preferable that the piezoelectric ceramic material hasmean crystal grain size of 0.9 μm or less, which makes the microscopicstructure of the electrodes homogeneous and makes it easier to reducethe residual stress.

[0020] Each piezoelectric ceramic layer in the laminated piezoelectricelement according to the present invention is preferably in a range from1 to 25 μm in thickness, which makes it possible to increase thedisplacement of the actuator.

[0021] When a voltage is applied between the electrodes, variations in dconstant are preferably within ±10% across the surface, which enables itto use a low-cost IC for controlling the displacement when a pluralityof displacement elements are mounted on a single circuit board.

[0022] In addition, bonding strength between the electrodes and thepiezoelectric ceramic layer is preferably 1.25 MPa or higher, whichmakes it easier to maintain stable piezoelectric characteristic.

[0023] The actuator of the present invention is characterized in that itis constituted from the laminated piezoelectric element described above,which makes it possible to make the actuator that has high reliabilityand better piezoelectric characteristic.

[0024] It is particularly preferable to join a support member to thebottom surface of the laminated piezoelectric element. This constitutionmakes it possible to reduce and stabilize variations in displacement.

[0025] Specifically, the actuator of the present invention comprises anoscillator plate, internal electrodes provided on the oscillator plate,piezoelectric ceramic layer provided on the internal electrodes and aplurality of surface electrodes provided on the piezoelectric ceramiclayer.

[0026] The printing head of the present invention comprises a flowpassage member in which a plurality of ink compressing chambers havingink nozzles are arranged and the actuator of claim 11 mounted on theflow passage member, the ink compressing chambers and said surfaceelectrodes is aligned with each other. Such a printing head has a betterdisplacement characteristic and is capable of printing with higherpicture quality and higher resolution.

[0027] Various objects and advantages of the present invention willbecome apparent in the course of the description, which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a schematic sectional view showing a laminatedpiezoelectric element of the present invention.

[0029]FIG. 2(a) is a schematic sectional view showing a printing headprovided with an actuator comprising the laminated piezoelectric elementof the present invention, and FIG. 2(b) is a plan view thereof.

[0030]FIG. 3 is a schematic sectional view showing a structure forevaluating the laminated piezoelectric element of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0031] Now the laminated piezoelectric element and an actuator of thepresent invention will be described in detail below with reference tothe accompanying drawings. FIG. 1 is a sectional view showing thelaminated piezoelectric element according to one embodiments of thepresent invention.

[0032] As shown in FIG. 1 the laminated piezoelectric element has alaminate of a plurality of piezoelectric ceramic layers 1 and electrodesprovided on the surface and inside of the laminate. The electrodescomprise internal electrode 2 stacked inside of the laminate and aplurality of surface electrodes 3 disposed on the surface of thelaminate. Thus a plurality of displacement elements consisting of thesurface electrodes 3, the internal electrodes 2 and the piezoelectricceramic layers 1 that are interposed between the electrodes are formed.The laminated piezoelectric element can be used preferably as anactuator by connecting lead wires to the surface electrodes 3 for theelectrical connection with the outside.

[0033] It is important that a total thickness T of the laminatedpiezoelectric element is 100 μm or less, preferably 85 μm or less andmore preferably 70 μm or less. This allows it to have a largerdisplacement of each displacement element and achieve high efficiency indriving the displacement elements with a low voltage.

[0034] The thickness t of the piezoelectric ceramic layer is from 1 to25 μm, preferably 3 to 22 μm, more preferably from 5 to 19 μm, and mostpreferably from 7 to 16 μm, in order to increase the displacement whileeffectively preventing cracks and breakage from occurring andmaintaining the shape.

[0035] The thin laminated piezoelectric element having a total thicknessof 100 μm or less of the prior art has been suffering significantdeformation resulting from firing, since the piezoelectric ceramic layeris too thin. Particularly in a laminated piezoelectric element whereinthe thickness of each piezoelectric ceramic layer is 25 μm or less, ithas been very difficult to suppress the displacement. Moreover, theresidual stress that is distributed unevenly has a marked effect on thed constant, thus resulting in unpredictable variations across a singlecircuit board. It has been especially difficult to control thedisplacement of the actuator, in the case of a laminated piezoelectricelement having a plurality of displacement elements mounted on a singlecircuit board.

[0036] According the present invention, in contrast, piezoelectriccharacteristic can be stabilized by improving the wettability of thesilver-palladium (Ag—Pd) electrodes and the piezoelectric ceramic layer,thereby increasing the bonding strength between these members. When anactuator consisting of the laminated piezoelectric element of thepresent invention shown in FIG. 1 is driven with an alternate signalhaving frequency of 20 KHz, for example, stable displacement is achievedand the problem of the prior art that oscillation stops in three hourscan be solved.

[0037] According to the present invention, it is important to use asilver-palladium alloy containing 71 to 99.9% by volume of silver and0.1 to 29% by volume of palladium as the electrodes, in order toincrease the bonding strength between the electrodes and thepiezoelectric ceramic layer. The electrode having such a composition hasbetter wettability with the piezoelectric ceramic material and isexpected to improve the bonding strength between these members.

[0038] In order to further decrease the residual stress between thepiezoelectric ceramic layer 1 and the electrodes 2, 3, lower limit ofthe silver content in the electrodes 2, 3 is preferably 80% by volume,more preferably 85% by volume, and most preferably 90% by volume. Upperlimit of the silver content is 99.9% by volume, preferably 97% byvolume, and more preferably 95% by volume.

[0039] Also according to the present invention, the electrodes made bysimultaneous firing preferably comprises a silver-palladium alloycontaining 87% or more by volume, preferably 90% or more by volume andmost preferably 93% or more by volume of silver, while controlling theresidual stress remaining in the actuator after firing within 100 MPa,preferably within 85 MPa and most preferably 70 MPa. By controlling thesilver content in the electrode to not less than 87% by volume, such aremarkable effect can be expected as the compressive stress due toshrinkage of the electrode is reduced. Also by controlling the residualstress in the actuator within 100 MPa, it is made possible to suppressthe decrease in capacitance of the piezoelectric ceramic layer andprevent the displacement of the displacement element from decreasing.

[0040] In order to further increase the bonding strength and reduce theresidual stress thereby improving the stability of the piezoelectriccharacteristic further, it is preferable that at least a part of theelectrodes, particularly the internal electrode 2, contains thepiezoelectric ceramic material. In order to increase the bondingstrength between the piezoelectric ceramic layer 1 and the electrodeswhile reducing the residual stress, proportion of the piezoelectricceramic material is preferably from 16 to 60% by volume of thesilver-palladium alloy, more preferably from 18 to 50% by volume andmost preferably from 20 to 30% by volume.

[0041] In order to achieve uniform distribution of the residual stress,it is preferable that the piezoelectric ceramic material has meancrystal grain size of 0.9 μm or less, more preferably 0.7 μm or less andmost preferably 0.6 μm or less. When the crystal grain size iscontrolled in the range described above, residual stress, if everexists, is distributed uniformly among the plurality of displacementelements, thereby minimizing the influence on the displacementcharacteristic through the reduction in the variation of the residualstress.

[0042] In the laminated piezoelectric element of the present invention,when a voltage is applied between the internal electrode 2 and thesurface electrode 3, the piezoelectric ceramic layer 1 interposedbetween the electrodes displaces. In case a plurality of displacementelements are formed on a single circuit board, it is made possible touse a low-cost IC for controlling the displacement element bysuppressing the variations in the d constant are preferably within ±10%across the surface, thereby reducing the cost of the unit including theactuator. In the laminated piezoelectric element of the presentinvention, since residual stress is reduced by increasing the bondingstrength of the electrodes and the piezoelectric ceramic layer, thevariations in the d constant can be controlled within ±10% across thesurface In addition, by setting the bonding strength between theinternal electrode 2 and the piezoelectric ceramic layer 1 to 1.25 MPaor higher, preferably to 2 MPa or higher and more preferably to 5 MPa orhigher, stable piezoelectric characteristic can be obtained and it ismade possible to suppress exfoliation of the piezoelectric ceramic layer1 and the electrodes 2, 3 that would lead to failure of driving, whendriving the actuator.

[0043] By combining the silver-palladium alloy and the piezoelectricceramic layer 1, it is made possible to suppress the deformation of thelaminated piezoelectric element and the variations of the d constantacross the surface, thereby to obtain the laminated piezoelectricelement that allows easy control of the displacement. The laminatedpiezoelectric element of the present invention can be appliedparticularly preferably to a device having a plurality of displacementelements mounted on a single circuit board. This constitution has anadvantage of making it easier to control the displacement and allow theuse of a low-cost IC.

[0044] In the present invention, the term piezoelectric ceramic materialrefers to a ceramic material that shows piezoelectricity, such as Bilayer compound, material having tungsten-bronze structure, alkaliniobate compound of perovskite structure, lead zirconate titanate (PZT)containing Pb and compound of perovskite structure containing leadtitanate. Among these materials, lead zirconate titanate containing Pband lead titanate are particularly preferable for improving thewettability and hence the bonding strength with the electrodes.

[0045] Specifically, a crystal containing Pb as a constituent element atsite A and Zr and/or Ti as constituent element at site B, and especiallymade of a lead zirconate titanate-based compound is preferable forobtaining a stable sintered piezoelectric material that has higher dconstant.

[0046] It is also preferable that the piezoelectric ceramic layer 1contains at least one kind selected from among Sr, Ba, Ni, Sb, Nb, Znand Te, which enables it to obtain the laminated piezoelectric elementhaving higher stability. Specifically, one made by solid solution ofauxiliary components Pb(Zn_(1/3)/Sb_(2/3))O₃ and Pb(Ni_(1/2)Te_(1/2))O₃may be used.

[0047] It is particularly desirable to further include an alkali earthelement as the constituent element at site A. As the alkali earthelement, Ba and Sr are particularly preferable since they enable it toachieve greater displacement. It is advantageous to include 0.02 to 0.08moles of Ba and 0.02 to 0.12 moles of Sr for achieving a largedisplacement in case the composition is dominated by tetragonal crystalsystem.

[0048] Specifically, for example, a material having composition ofPb_(1-x-y)Sr_(x)Ba_(y)(Zn_(1/3)Sb_(2/3))_(a)(Ni_(1/2)Te_(1/2))_(b)Zr_(1-a-b-c)Ti_(c)O₃+αwt% Pb_(1/2)NbO₃(0≧x≧0.14, 0≧y≧0.14, 0.05≧a≧0.1, 0.002≧b≧0.01,0.44≧c≧0.50, α=0.1˜1.0) may be used.

[0049] Now the method of manufacturing the laminated piezoelectricelement of the present invention will be described below in the case ofusing PZT as the piezoelectric ceramic material, by way of example.

[0050] First, PZT powder having purity of 99% and mean particle size of1 μm or less is prepared as the material to make the piezoelectricceramic material.

[0051] A mixture of the piezoelectric ceramic powder and an organicbinder is formed into the shape of tape, to make a plurality of greensheets. Some of the green sheets are coated with an Ag—Pd paste thatmakes the internal electrode on part thereof, with the green sheetsbeing stacked one on another and cut into a desired shape. Theselaminates are heated to around 400° C. to remove the binder, and thenfired at a temperature from 900 to 1050° C. Then the surface electrodeis formed on the surface, and the piezoelectric ceramic layer betweenthe internal electrodes and the surface electrode is subjected topolarization, thereby to complete the laminated piezoelectric element.

[0052] When fabricating the laminate of the green sheets, it ispreferable to attach constraint sheet, that comprises the piezoelectricceramic material of substantially the same composition as that of thegreen sheet and an organic composition, on one or both of the laminateand pressed together. Restricting the outside green sheet from shrinkingby means of the constraint sheet has an effect of suppressing the warpof the laminate, thus enabling it to reduce the stress generated thereinwhen bonding it with a supporting substrate.

[0053] Density of the green sheet before sintering is preferably 45g/cm² or higher. By increasing the density of the sintered material to4.5 g/cm² or higher, it is made possible to sinter at a lowertemperature. When the density of the green sheet is increased further,Pb can be restricted from evaporating.

[0054] The actuator of the present invention is provided with thelaminated piezoelectric element described above, and is featured by thecapability to make a large displacement. It is particularly preferablethat the laminated piezoelectric element described above is bonded ontothe supporting substrate.

[0055] The actuator of the present invention has a plurality ofdisplacement elements mounted on a single circuit board, and can bepreferably applied to an ink jet printing head used in an apparatus thatutilizes the ink jet technology.

[0056] In the ink jet printing head shown in FIG. 2(a), (b), forexample, an actuator 15 is bonded to a flow passage member 16 that has aplurality of ink compressing chambers 16 a having ink nozzles 18 and apartition walls 16 b that separate the ink compressing chambers 16 a.Thus this printing head has such a constitution as the actuator 15 isplaced on the flow passage member 16 wherein the plurality of inkcompressing chambers 16 a having the ink nozzles 18 are arranged, withthe ink compressing chambers 16 a and the surface electrode 13 beingaligned with each other.

[0057] The actuator 15 is made by forming the internal electrode 12 onone of the principal surfaces of the piezoelectric ceramic layer 11 b,forming the surface electrode 13 on the other principal surface, andforming the displacement elements 14, that comprise the surfaceelectrode 13, the internal electrode 12 and piezoelectric ceramic layer11 a interposed between these electrodes, on an oscillator plate 11.

[0058] Specifically, the actuator 15 comprising the internal electrode12, the piezoelectric ceramic layer 11 b having a thickness of 50 μm orless and the surface electrode 13 that are stacked in this order on theoscillator plate 11 a, and a plurality of the surface electrodes 13 thatare disposed on the surface of the piezoelectric ceramic layer 11 b, isbonded onto the flow passage member 16 so that the surface electrodes 13are located right above the ink compressing chambers 11. The abovepiezoelectric ceramic material can be used as the oscillator plate 11 a.

[0059] With this printing head, when a voltage is applied by a drivecircuit between one of the surface electrodes 13 and the internalelectrode 12, the piezoelectric ceramic layer 11 b located right belowthe particular surface electrode 13 is displaced so as to apply apressure to the ink in the ink compressing chamber 13 a, so that a dropof ink is discharged from an ink outlet orifice 18 that opens at thebottom of the flow passage member 16.

[0060] By using the laminated piezoelectric element of the presentinvention as the actuator of the printing head, the printing head can bemade by using a low-cost IC.

[0061] The printing head according to the present invention has betterdisplacement characteristic that enables it to discharge the ink at ahigher speed with higher precision, and is preferably used for highspeed printing. A printer that comprises the printing head according tothe present invention, an ink tank which supplies ink to the printinghead and a paper transfer mechanism is capable of printing at a higherspeed with higher precision more easily than the prior art.

[0062] The following examples illustrate the manner in which the presentinvention can be practiced. It is understood, however, that the examplesare for the purpose of illustration and the invention is not to beregarded as limited to any of the specific materials or conditiontherein.

EXAMPLE 1

[0063] The laminated piezoelectric element of the present invention wasfabricated and was applied to an ink jet printing head as an actuator.

[0064] First, a powder of piezoelectric ceramic material containing leadzirconate titanate (PZT) having purity of 99% or higher was prepared asthe starting material.

[0065] The piezoelectric ceramic powder was mixed with butylmethacrylate used as an aqueous binder, ammonium polycarbonate used as adispersant and isopropyl alcohol and water used as solvents, to obtain aslurry. The slurry was spread over a carrier film by means of a doctorblade, so as to form a green sheet having a thickness of 30 μm.

[0066] Then a paste to form the internal electrode was made by mixing aAg—Pd alloy containing silver and palladium in proportions shown inTable 1 and the piezoelectric ceramic powder containing PZT as the maincomponent, thereby to obtain the composition of the internal electrodeshown in Table 1. The Ag—Pd alloy and the piezoelectric ceramic powderwere added to separate vehicles that contained organic binder andorganic solvent, and were well mixed to obtain the paste to make theinternal electrode.

[0067] The paste was applied to the surface of the green sheet to athickness of 4 μm by printing, thereby forming the internal electrode.Then, two green sheets without any internal electrode, the green sheetwith the internal electrode on the surface, and the green sheet withoutany internal electrode were stacked in this order, and pressed to make alaminate.

[0068] The laminate, after being degreased, was sintered by keeping atthe sintering temperature shown in Table 1 for two hours in anatmosphere having oxygen concentration of 99% or higher, thereby makinga sintered laminate consisting of the piezoelectric ceramic layer 1 andthe internal electrodes 2. Then the surface electrode 3 was formed onone surface of the sintered laminate by applying Au paste by the screenprinting process and firing at a temperature from 600 to 800° C. in airatmosphere. 600 points of the surface electrode 3 were formed on onesubstrate.

[0069] Last, lead wires were connected to the surface electrodes 3 bysoldering, thus completing the laminated piezoelectric element havingthe configuration shown in FIG. 1.

[0070] Samples used in measuring the d constant and bonding strengthwere fabricated as described below. The laminated piezoelectric elementmade as described above was formed into 10 cm square, that was polishedonly on one side thereof, leaving only one layer of the piezoelectricceramic material. Electrodes were formed by vapor deposition of Au onboth surfaces of this ceramic sheet. The ceramic sheet was then cut intostrips measuring 12 mm by 3 mm by dicing, and the strips were subjectedto polarization by applying DC voltage of 3 kv/mm in silicone oil.Resonance frequency, antiresonance frequency, resonance resistance,antiresonance resistance and capacitance of the elements thus obtainedwere measured using an impedance analyzer (Agilent Technologies' model4194A), and the value of d31 was determined using a value of densitydetermined by Archimedes' method. The values of d31 were averaged andmaximum percent deviation from the mean value was taken as the variationof d31.

[0071] Displacement was measured using the setup shown in FIG. 3,wherein the actuator comprised a plurality of displacement elements 24,that were made by interposing the piezoelectric ceramic layer 21 bbetween the surface electrode 23 and the internal electrodes 22,disposed on an oscillator plate 21 a, with the actuator being bondedonto a supporting member 26 having grooves 26 a and partition walls 26b.

[0072] The actuator was irradiated with laser beam on the side where thegroove 26 a are formed by means of a laser Doppler displacement meter,so as to measure displacements at the center and seven points along theperiphery of the groove 26 a, and the displacements were averaged.

[0073] Electrode resistance was measured between two VIA electrodesconnected to the internal electrodes using the impedance analyzer(Agilent Technologies' model 4194A) at 25° C.

[0074] For the bonding strength, tensile test was conducted on thelaminate from which the binder has not been removed, having partialelectrode measuring 2 mm by 2 mm made of the same material as that ofthe internal electrode printed thereon, that was fired under the sameconditions as described above, then a Cu wire 0.8 mm in diameter wasconnected to the partial electrode measuring 2 mm by 2 mm by soldering.The test result is shown in Table 1. TABLE 1 Thickness Internalelectrode composition Each Ag—Pd alloy Ceramic powder com- Ag Pd Contentgrain ponent Firing Variations Displace- Electrode Bonding Sample % by %by % by size layer Total temp. of d31 ment resistance strength No.volume volume volume μm μm μm ° C. % nm Ω MPa/mm² 1 99.9 0.1 25 0.5 25100 900 2 85 2 14.2 2 97 3 25 0.5 25 100 950 2 86 2 15.1 3 95 5 25 0.525 100 960 2 85 2 14.1 4 90 10 25 0.5 25 100 1000 2 85 2 15.2 5 85 15 250.5 25 100 1000 2 85 2 13.1 6 80 20 25 0.5 25 100 1000 3 86 2 10.1 7 7525 25 0.5 25 100 1000 5 85 2 5.2 * 8 70 30 25 0.5 25 100 1000 11 86 21.1 * 9 65 35 25 0.5 25 100 1000 15 85 2 0.4 10 80 20 10 0.5 25 100 100010 85 2 5.1 11 80 20 16 0.5 25 100 1000 3 86 2 6.2 12 80 20 20 0.5 25100 1000 2 85 2 7.1 13 80 20 30 0.5 25 100 1000 2 85 2 14.1 14 80 20 400.5 25 100 1000 2 85 2 14.1 15 80 20 50 0.5 25 100 1000 2 86 2 15.2 1680 20 60 0.5 25 100 1000 2 85 2 15.1 17 80 20 70 0.5 25 100 1000 2 86 3015.2 18 80 20 80 0.5 25 100 1000 2 86 1000 14.1 19 80 20 25 0.6 25 1001000 3 86 2 10.1 20 80 20 25 0.8 25 100 1000 3 86 2 10.3 21 80 20 25 0.925 100 1000 3 86 2 10.2 22 80 20 25 1.0 25 100 1000 10 85 2 10.3 23 8020 25 0.5 12 48 1000 2 85 2 10.1 24 80 20 25 0.5 15 60 1000 2 86 2 10.225 80 20 25 0.5 18 72 1000 2 85 2 10.1 26 80 20 25 0.5 20 80 1000 2 86 210.1 27 80 20 25 0.5 25 100 1000 2 85 2 10.2 * 28   80 20 25 0.5 30 10001000 2 20 2 10.1

[0075] Samples Nos. 1 to 7 and Nos. 10 to 27 of the present inventionwere laminated piezoelectric elements showing variations of d31 within10% and bonding strength of 5 MPa/mm² or higher, allowing it to easilycontrol the displacement.

[0076] Samples Nos. 8 and 9, out of the scope of the present invention,that contained 70% by volume or less silver showed significant variationin d31 of 11% or more and low bonding strength of 1.26 MPa/mm² or less.

[0077] Sample No. 28, out of the scope of the present invention, havinga total thickness of 1000 μm (1 mm) showed very low displacementcharacteristic with a low displacement of 20 nm.

EXAMPLE 2

[0078] High purity powders of Pb₂O₃, ZrO₂, TiO₂, BaCO₃, ZnO, SrCO₃,Sb₂O₃, NiO, TeO₂ were prepared as the stock materials. Predeterminedquantities of these powders were measured to obtain the compositions A1to D1 described below after sintering.

[0079] [A1]:Pb_(1-x-y)Sr_(x)Ba_(y)(Zr_(1/3)Sb_(2/3))_(a)(Ni_(1/2)Te_(1/2))Zr_(1-a-b-c)Ti_(c)O₃(X=0.04,y=0.02, a=0.075, b=0.005, c=0.45)

[0080] [B1]:Pb(Zn_(1/3)Sb_(2/3))_(0.075)(Ni_(1/3)Te_(1/2))_(0.005)Zr_(0.47)Ti_(0.04)O₃

[0081] [C1]: PbZr_(0.5)Ti_(0.5)O₃

[0082] [D1]: BaTiO₃

[0083] The predetermined quantities of the powders measured as describedabove were mixed in wet process in a ball mill for 20 hours, and themixture was dewatered and dried. The dried mixture was calcined at 900°C. for three hours, and the calcined material was crushed in wet processin a ball mill.

[0084] The crushed material was mixed with an organic binder, water, adispersant and a plasticizer to make a slurry. The slurry was formedinto a sheet by the roll coater process that is commonly employed whenforming a thin green sheet, thereby making a green sheet. The thicknessof the green sheet was set by taking the shrinkage ratio intoconsideration so that the thickness shown in Table 2 could be achievedafter firing.

[0085] The green sheet was punched through using a die to make aplurality of rectangular sheets. The paste containing the Ag—Pd alloywas applied to the surface of the rectangular sheets by screen printing,thereby forming the internal electrodes and the surface electrodes.

[0086] The green sheets coated with the electrode paste and the greensheets without the electrode paste were stacked one on another as shownin FIG. 1, and were pressed while heating so as to fuse together,thereby making the laminate.

[0087] After degreasing the laminate at 400° C., the laminate was firedunder the conditions shown in Table 1 for two hours, thereby making theactuator.

[0088] After polishing the cross section of the ceramic layers, thethickness of the actuator was measured by means of a microscope. Bondingof the piezoelectric ceramic layer and the electrodes was visuallychecked to see if there was exfoliation.

[0089] Residual stress in the actuator was measured by means of X-raydiffraction with characteristic X-ray of Fe and diffraction peak of126°, using collimator having diameter of 2 mm. Residual stress is givenwith a negative sign if it is a compressive stress.

[0090] Displacement was measured similarly to Example 1, with theresults shown in Table 2. TABLE 2 Internal Thickness Piezo- electrodeCondition of firing Each electric composition Oxygen com- Actuatorceramic Ag Pd concen- ponent Residual Displace- Exfoliation Sample layer% by % by temp. tration layer Total stress ment of the No. kind volumevolume ° C. % μm μm MPa nm elecrtodes 29 A1 70 30 1000 98 11 60 −150 22no 30 A1 80 20 1000 98 11 60 −110 48 no 31 A1 87 13 1000 98 11 60 −90 60no 32 A1 90 10 1000 98 11 60 −70 72 no 33 A1 93 7 980 98 11 60 −55 80 no34 A1 95 5 960 98 11 60 −50 82 no 35 A1 97 3 950 98 11 60 −30 77 no 36A1 99 1 930 98 11 60 −20 70 no 37 A1 90 10 1000 98 60 50 −100 40 no 38A1 90 10 1000 98 50 50 −90 50 no 39 A1 90 10 1000 98 20 50 −80 60 no 40A1 90 10 1000 98 15 50 −75 70 no 41 A1 90 10 1000 98 5 50 −67 75 no 42A1 90 10 1000 98 3 50 −70 80 no 43 A1 90 10 950 98 11 45 −78 68 no 44 A190 10 900 98 11 45 −80 65 no 45 A1 90 10 1000 95 11 50 −80 68 no 46 B190 10 1000 98 11 50 −80 55 no 47 C1 90 10 1000 98 11 50 −75 50 no 48 D190 10 1000 98 11 50 −80 30 no * 49   A1 90 10 1000 98 20 200 −85 15 no

[0091] Table 2 shows that samples Nos. 29 to 45 of the present inventionhaving composition A1 showed displacements of 20 nm or larger. SamplesNos. 31 to 45 having Ag content of 87% by volume or higher and residualstress of 100 MPa or less showed displacements of 40 nm or larger.Samples Nos. 32 to 36 and Nos. 39 to 45 having residual stress of 85 MPaor less, in particular, showed displacements of 60 nm or larger. SamplesNos. 32 to 36 and Nos. 40 to 42 having residual stress of 75 MPa or lessshowed displacements of 70 nm or larger.

[0092] Samples Nos. 46 to 48 of the present invention havingcompositions B1, C1 and D1 showed displacements of 30 nm or larger.

[0093] Samples No. 49 having composition A1 but 200 μm thick, incontrast, showed small displacement of 15 nm.

What is claimed is:
 1. A laminated piezoelectric element having athickness of 100 μm or less, comprising a laminate which comprises aplurality of piezoelectric ceramic layers, and electrodes provided atleast one of the surface and the inside of said laminate, wherein saidelectrodes comprises a silver-palladium alloy containing 71 to 99.9% byvolume of silver and 0.1 to 29% by volume of palladium.
 2. The laminatedpiezoelectric element according to claim 1, wherein said electrodescomprises a silver-palladium alloy containing 87% by volume or moresilver, and residual stress remaining inside is 100 MPa or less.
 3. Thelaminated piezoelectric element according to claim 1, wherein saidpiezoelectric ceramic layer contains Pb.
 4. The laminated piezoelectricelement according to claim 1, wherein said electrodes contains apiezoelectric ceramic material, and the proportions of thesilver-palladium alloy to the piezoelectric ceramic material are in arange from 100: 16 to
 60. 5. The laminated piezoelectric elementaccording to claim 4, wherein said piezoelectric ceramic material has amean crystal grain size of 0.9 μm or less.
 6. The laminatedpiezoelectric element according to claim 1, wherein each piezoelectricceramic layer is in a range from 1 to 25 μm in thickness.
 7. Thelaminated piezoelectric element according to claim 1, wherein variationsin d constant is within ±10% across the surface when a voltage isapplied between the electrodes.
 8. The laminated piezoelectric elementaccording to claim 1, wherein a bonding strength between said electrodesand said piezoelectric ceramic layer is 1.25 MPa or higher.
 9. Anactuator comprising the laminated piezoelectric element of claim
 1. 10.The actuator according to claim 9, wherein a supporting member is bondedonto the bottom surface of said laminated piezoelectric element.
 11. Anactuator comprising an oscillator plate, internal electrodes provided onsaid oscillator plate, a piezoelectric ceramic layer provided on saidinternal electrodes and a plurality of surface electrodes provided onsaid piezoelectric ceramic layer, wherein said oscillator plate, saidinternal electrodes, said piezoelectric ceramic layer and said surfaceelectrodes comprise the laminated piezoelectric element of claim
 1. 12.A printing head comprising a flow passage member in which a plurality ofink compressing chambers having ink nozzles are arranged and theactuator of claim 11 mounted on the flow passage member, wherein the inkcompressing chambers and said surface electrodes is aligned with eachother.